U.S. patent number 4,611,181 [Application Number 06/772,148] was granted by the patent office on 1986-09-09 for temperature compensated oscillator with reduced noise.
This patent grant is currently assigned to NEC Corporation. Invention is credited to Yukio Fukumura, Takashi Matsuura.
United States Patent |
4,611,181 |
Fukumura , et al. |
September 9, 1986 |
Temperature compensated oscillator with reduced noise
Abstract
A temperature-compensated oscillator avoids noise heretofore
caused by unduly high signal level changes of a control voltage
resulting from sensed temperature changes. This is done by reducing
the high level changes into a plurality of relatively low level
changes which produce a cumulative effect comparable to the high
level effect. The many low level changes do not produce reactions
which are abrupt enough to cause noise, especially a phase
modulation or frequency modulation noise.
Inventors: |
Fukumura; Yukio (Tokyo,
JP), Matsuura; Takashi (Tokyo, JP) |
Assignee: |
NEC Corporation (Tokyo,
JP)
|
Family
ID: |
16236043 |
Appl.
No.: |
06/772,148 |
Filed: |
September 3, 1985 |
Foreign Application Priority Data
|
|
|
|
|
Sep 10, 1984 [JP] |
|
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59-189138 |
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Current U.S.
Class: |
331/66;
331/176 |
Current CPC
Class: |
H03L
1/025 (20130101) |
Current International
Class: |
H03L
1/02 (20060101); H03L 1/00 (20060101); H03L
001/02 () |
Field of
Search: |
;331/66,69,70,176
;219/209,210 ;73/766,497 ;364/557,571,574 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: LaRoche; Eugene R.
Assistant Examiner: Mis; D. C.
Attorney, Agent or Firm: Laff, Whitesel, Conte &
Saret
Claims
What is claimed is:
1. A temperature-compensated oscillator device comprising:
temperature sensing section means including temperature sensor
means for sensing an ambient temperature to provide a temperature
data signal representative of the sensed temperature,
analog-to-digital converter means for converting the temperature
data signal into a first digital signal having a first variable
digital value;
control section means for converting the first digital signal into
a second digital signal having a second digital value, the control
section means comprising first means for converting a variation in
the first digital value into a plurality of time-divided fractional
variations in the second digital value; and
oscillating section means including a converter means for
converting the second digital signal into a frequency control
signal, and voltage-controlled oscillator means responsive to the
frequency control signal for changing the oscillation signal
frequency.
2. A temperature-compensated oscillator device as claimed in claim
1, wherein said first means comprises second means responsive to
the first digital signal for providing a third digital signal
corresponding thereto; third means for comparing the second digital
signal with the third digital signal and for providing an
identification signal indicative of whether the second and third
digital signals are coincident with each other and a discrimination
signal indicative of which one of the second and third digital
signals is greater than the other; and fourth means responsive to
the identification signal, the discrimination signal and a clock
signal for stopping a count of the clock signal when the
identification signal indicates coincidence, and said fourth means
incrementing or decrementing the count in accordance with the
discrimination signal when the identification signal indicates
non-coincidence, thereby providing the second digital signal.
3. A temperature-compensated oscillator device as claimed in claim
2, wherein the second means comprises a read only memory, the third
means comprising a digital comparator, and the fourth means
comprising an up/down counter.
4. A temperature-compensated oscillator device as claimed in claim
1, wherein said first means comprises second means responsive to
the first digital signal for providing a third digital signal
corresponding thereto; third means for comparing the second digital
signal with the third digital signal and for providing an
identification signal indicative of whether the second and third
digital signals are coincident with each other and a discrimination
signal indicative of which one of the second and third digital
signals is greater than the other; fourth means for controlling the
passing of a clock signal in response to the identification signal;
and fifth means for counting the output of the fourth means in
response to the discrimination signal.
5. A temperature-compensated oscillator device as claimed in claim
4, wherein the second means comprises a read only memory, the third
means comprises a digital comparator, the fourth means comprises a
gate circuit and the fifth means comprises an up/down counter.
6. A temperature-compensated oscillator comprising means for
producing a temperature data signal responsive to sensed
temperature changes, control means for converting said temperature
data signal into control signals in order to compensate the
temperature induced changes in the operation of said oscillator,
said control signals being large enough to cause noise, means for
subdividing said control signals into fractional variations which
are small enough to greatly reduce said noise, said control means
comprises counter means having a first output, memory means for
providing a digital signal responsive to said temperature data
signal, comparator means for comparing said digital signal with the
first output of said counter means, a source of clock pulses for
stepping said counter until said comparator means finds a parity,
each step of said counter changing said control signal by an
incremental amount to produce one of said fractional
variations.
7. The temperature-compensated oscillator of claim 6 wherein said
memory means is a read only memory means.
8. The temperature-compensated oscillator of claim 6 wherein said
counter is an up/down counter which is driven bi-directionally
responsive to the direction of changes in said temperature.
9. The temperature-compensated oscillator of claim 6 further
comprising gate means jointly responsive to said comparator and to
said source of clock pulses, and means responsive to the output of
said gate for said stepping of said counter.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a temperature-compensated
oscillation device and, more particularly, to a digitally
controlled temperature-compensated oscillation device.
A digitally controlled, temperature-compensated oscillation device
has been extensively used as a local oscillator of a mobile radio
apparatus because its frequency generally remains stable over a
wide temperature range. Such a type of oscillation device comprises
a temperature sensing section including a temperature sensor and an
analog-to-digital (AD) converter, a read only memory (ROM) which
stores compensation data associated with outputs of the AD
converter, and an oscillating section responsive to an output of
the ROM and comprising a digital-to-analog (DA) converter and a
voltage controlled oscillator (VCO).
The problem with an oscillation device having the above
construction is that a noticeable variation in ambient temperature
causes an output of the AD converter, i.e., an output value of the
ROM, to vary sharply for a moment to add frequency modulation noise
and phase modulation noise to an output of the VCO. In a
multichannel communication system, these noises consitute a source
of noise for other channels. That noise on other channels requires
the exclusive frequency band to have an undesirable width.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a
digitally controlled, temperature-compensated oscillation device
which reduces the previously mentioned kinds of noise.
A temperature-compensated oscillator device to which the present
invention is applicable, comprises temperature sensing section
means including temperature sensor means for sensing an ambient
temperature. A temperature data signal is provided which is
representative of the sensed temperature. An analog-to-digital
converter means converts the temperature data signal to a first
digital signal having a first digital value. A control section
means converts the first digital signal into a second digital
signal having a second digitial value. An oscillating section means
includes converter means for converting the second digital signal
into a frequency control signal and voltage-controlled oscillator
means responsive to the frequency control signal for changing the
oscillation signal frequency. According to the present invention,
the control section means comprises first means for converting a
variation in the first digital value to a plurality of time-divided
fractional variations in the second digital value.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects, features and advantages of the present
invention will become more apparent from the following detailed
description taken with the accompanying drawings in which:
FIG. 1 is a block diagram of a prior art temperature-compensated
oscillation device;
FIGS. 2A-2C are graphs representative of the operation of a
voltage-controlled oscillator which is applicable to the present
invention as well as to the prior art, specifically FIG. 2A shows
an oscillation signal frequency variation against ambient
temperature characteristic, FIG. 2B shows an oscillation signal
frequency variation against frequency control signal
characteristic, and FIG. 2C shows a frequency control signal
against ambient temperature characteristic;
FIG. 3 is a graph showing an oscillation signal frequency variation
against an ambient temperature characteristic of a prior art
temperature-compensated oscillation device and against the
inventive oscillation device;
FIG. 4 is a graph showing an oscillation signal frequency variation
against a time characteristic of the prior art
temperature-compensated oscillation device;
FIG. 5 is a block diagram of a temperature-compensated oscillation
device embodying the present invention;
FIG. 6 is an oscillation signal frequency variation against a time
characteristic which is particular to the temperature-compensated
oscillation device of the present invention; and
FIG. 7 is a block diagram showing another embodiment of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
To better understand the present invention, a brief reference will
be made to a prior art, digitally controlled oscillation device,
shown in FIG. 1. As shown, the device comprises a temperature
sensing section 1 made of a temperature sensor 11 and an
analog-to-digital (AD) converter 12, a read only memory (ROM) 21,
and an oscillating section 3 made of a digital-to-analog (DA)
converter 31 and a voltage-controlled oscillator (VCO) 32. The VCO
32 comprises a crystal oscillator and a variable capacitance
element.
The temperature sensor 11 senses an ambient temperature and
converts it to a voltage which is applied as a temperature data
signal on wire 101 to the AD converter 12. The AD converter 12
quantizes the input signal on wire 101 to provide a first digital
value which is produced as a first digital signal applied to bus
102. This signal on bus 102 is delivered to an address input
terminal of the ROM 21 to specify a particular ROM address. A
second digital value which is stored at that address is outputted
as a second digital signal via data bus 205a. The DA converter 31
to which the second digital signal is routed via bus 205a
transforms the second digital signal into a voltage and applies
that voltage as a frequency control signal via wire 301 to the VCO
32. Responsive to the signal on wire 301, the VCO 32 controls the
capacitance of its variable capacitance element. As a result, there
is a temperature-compensation of the frequency of an oscillation
signal applied to wire 302, which is an output of the VCO 32.
Details of the temperature compensation which is effected, as
described above, will be described with reference to FIGS. 2A-2C.
While the frequency control signal on wire 301 is maintained at a
certain constant value, the frequency of the oscillation signal at
302 may vary with the ambient temperature as shown in FIG. 2A.
Specifically, the graph of FIG. 2A represents a relationship
between the temperature surrounding the crystal oscillator of the
VCO 32 and the variation of its resonance frequency. Meanwhile,
when the ambient temperature remains constant, the frequency of the
oscillation signal at 302 may vary with the frequency control
signal appearing on wire 301, as shown in FIG. 2B. If the
relationship between the first digital signal on data bus 102 and
the second digital signal on data bus 205a in the ROM 21 has the
relationship shown in FIG. 2C between the ambient temperature and
the frequency control signal on wire 301, the frequency of the
oscillation signal at 302 is temperature-compensated. A step curve
is shown in FIG. 2C because the ambient temperature is quantized as
the first digital signal on wire 102.
FIG. 3 shows the frequency variation of the oscillation signal at
302, after temperature compensation, relative to the ambient
temperature. Comparing FIG. 3 with FIG. 2A, it will be seen that as
a result of temperature compensation, the frequency variation of
the oscillation signal at 302 has been reduced by about one-quarter
over the temperature range of -20.degree. C. to +60.degree. C.
FIG. 4 shows a graph which is representative of exemplary frequency
variations of the oscillation signal at 302, with respect to time.
These frequency variations occur while the ambient temperature is
varied with time. As understood by comparing FIG. 4 with FIGS. 2A
and 2C, the ambient temperature shown in FIG. 4 increases with
time. A temperature T.sub.1 is associated with a time t.sub.1 and a
temperature T.sub.2 with a time t.sub.2. During the period between
the times t.sub.1 and t.sub.2, the frequency control signal on wire
301 remains at a constant voltage V.sub.1 and the frequency of the
oscillation signal at 302 increases with time. At the time t.sub.2,
the signal on wire 301 shifts from the voltage V.sub.1 to a voltage
V.sub.2. At this moment, the frequency of the signal at 302 is
sharply lowered. In this manner, at the moment when the output of
the AD converter 12 is varied, the frequency of the oscillation
signal at 302 is sharply varied with a result that frequency
modulation noise and phase modulation noise are added to the signal
at 302.
Thus, in this prior art device, there is a sufficiently small
frequency variation in the digitally temperature-controlled
oscillation device installed in a radio frequency or phase
modulation communcation system. However, the prior art cannot avoid
a substantial magnitude of noise, as previously discussed. In
addition, the influence of the noise extends into other
channels.
FIG. 5 shows a temperature-compensated oscillation device embodying
the present invention, which is free from the drawbacks stated
above. As shown, the oscillation device comprises a temperature and
an AD converter 12. A control section 2 is made of a ROM 21, a
comparator 22 and an up-down counter 23. An oscillating section 3,
is made of a DA converter 31 and a VCO 32. The VCO 32 comprises a
crystal oscillator and a variable capacitance element.
The temperature sensor 11 converts an ambient temperature into a
voltage and produces the voltage as a temperature data signal at
101. Responsive to the signal at 101, the AD converter 12 quantizes
it to provide a first digital value which is applied to data bus
102 as the first digital value signal to an address input terminal
of the ROM 21. The ROM 21 produces a third digital value (assumed
to have a value A) from a particular address thereof which is
specified by the input signal on data 102, the third digital value
being applied over data bus 201 to one input terminal of the
comparator 22. Applied to the other input terminal of the
comparator 22 is a count from the up-down counter 23 (assumed to
have a value B).
The comparator 22 produces an identification signal at 202 which is
a high level "1" when A=B and a low level "0" when A.noteq.B. The
comprator 22 also produces a discrimination signal at 203 which is
a high level "1" when A>B and a low level "0" when A<B. The
identification signal at 202 and the discrimination signal at 203
are applied to the up-down counter 23. A clock signal on wire 204
is also applied to the up-down counter 23 via a clock input
terminal 24 of the control section 2.
While the identification signal at 202 is a high level, the counter
23 is disenabled to maintain the value B equal to the value A.
While the identification signal at 202 is a low level and the
discrimination signal at 203 is a high level, the counter 23 is
incremented responsive to each pulse of the clock signal appearing
on wire 204. When the identification signal at 202 is a low level
and the discrimination signal at 203 is a high level, the counter
23 is decremented responsive to each pulse of the clock signal on
wire 204. In this manner, the comparator 22 and the counter 23
cooperate with each other to maintain the value B equal to the
value A when A=B and to increment or decrement the value B to the
value A when A.noteq.B.
The output of the counter 23 is also applied to the data bus 205
and thus to the DA converter 31. The DA converter 31 converts the
input signal on bus 205 into a voltage and applies it to the VCO
via wire 301 as a frequency control signal. The signal on wire 301
controls the capacitance of the variable capacitance element of the
VCO 32 to temperature-compensate the frequency of an oscillation
signal at 302 which is outputted from the oscillatin device.
Thus, the control section 2 converts a variation in the first
digital signal appearing on data bus 102 into a plurality of
time-divided fractional variations in the output of the counter 23
which appears on data bus 205.
FIG. 6 shows an exemplary relationship between time and the
frequency variation of the oscillatin signal at 302, in accordance
with the illustrative embodiment of FIG. 5, the temperature being
assumed as varying with time. Assume that a value A is associated
with an ambient temperature at a time immediately before a time
t.sub.1 is A.sub.1, and further, assume that the value A.sub.1 has
changed to A.sub.2 at the time t.sub.1. Then, the value B changes
from A.sub.1 to (A.sub.1 -1) at the time t.sub.1 to (A.sub.1 -2) at
a time (t.sub.1 +t.sub.c), and to (A.sub.1 -3) at a time (t.sub.1
+2t.sub.c), where t.sub.c is the period of the clock signal
appearing on wire 204. In the example shown in FIG. 6, A.sub.2 is
equal to (A.sub.1 -3). As the value B is varied at the times
t.sub.1, (t.sub.1 +t.sub.c) and (t.sub.1 +2t.sub.c), the frequency
of the oscillation signal at 302 is also varied in a stepwise
manner at those times. Comparing FIG. 6 with FIG. 4, it will be
apparent that the stepwise variations, i.e., the amounts of sharp
variations of the frequency of the signal at 302 are smaller in the
illustrative embodiment (FIG. 6) than in the prior art (FIG. 4). As
a result, less noise is introduced into the signal at 302 due to
the sharp frequency variations.
FIG. 7 shows another embodiment of the present invention. The
oscillation device in this particular embodiment differs from that
of FIG. 5 in that the up-down counter 23 of FIG. 5 is replaced by a
gate 25 and an up-down counter 26. The identification signal on
wire 202 and clock signal on wire 204 are applied to the gate 25.
Specifically, when the identification signal at 202 is a low level,
the gate 25 is enabled to pass the clock signal 204 to the up-down
counter 26, as an output signal at 206. When the signal at 202 is a
high level, the gate 25 is disenabled to interrupt the supply of
the clock signals at 204 to the counter 26. As labeled 23a in the
drawing, the gate 25 and the counter 26 form a circuit which
cooperates to fulfill the function which is assgned to the counter
23 of the first embodiment. Hence, the embodiment of FIG. 7 is the
same in operation and effect as the embodiment of FIG. 5.
In summary, it will be seen that the present invention provides a
temperature-compensated oscillation device which reduces the
frequency variations and the noise over a wide temperature range.
Hence, a radio communication apparatus which is implemented with
the inventive device narrows the exclusive frequency band width, as
compared to the band width required by a prior art apparatus.
Various modifications will become possible for those skilled in the
art, after they have received the teachings of the present
disclosure, without departing from the scope thereof. For example,
ROM 21 is used in the illustrative embodiments as a numerical value
conversion means for converting the first digital signal at 102
into the third digital signal at 201. However, such a function may
alternatively be fulfilled by means of a memory which generates a
constant of a polynominal for converting a first digital value to a
second digital value, and an operation unit for operating
responsive to the polynomial. Such a conversion means is disclosed
in Japanese Unexemined Patent Publication (Kokai) 58-184809, for
example. Further, in the illustrative embodiments, as well as in
the modification mentioned above, the crystal oscillator included
in the VCO 32 may be replaced with an elastic surface wave element.
In addition, in all the embodiments and their modifications
described, the clock signal input terminal 24 may be omitted.
Instead, a clock signal generator may be added to the control
section 2, in which case the output of the clock signal generator
will serve as the source of the clock signal at 204.
Those who are skilled in the art will readily perceive how to
modify the invention. Therefore, the appended claims are to be
construed to cover all equivalent structures which fall within the
true scope and spirit of the invention.
* * * * *